Solid core golf balls are well known in the art. Typically, solid cores comprise a crosslinked polybutadiene rubber material, which provides the primary source of resiliency for the golf ball. Further increase in core resiliency can be achieved by increasing the cross-link density of the polybutadiene. The core is typically protected by a cover, and may comprise additional layers in between, such as outer core layers, intermediate layers, or inner cover layers. One or more of these additional layers may be a wound layer of tensioned elastic windings.
A known drawback of polybutadiene cores cross-linked with zinc diacrylate is that zinc diacrylate is adversely affected by moisture. Water moisture vapor reduces the resiliency of the cores and degrades its properties. A polybutadiene core will absorb water and loose its resilience. It is beneficial to apply a cover layer over the core shortly after core molding to maintain optimum ball properties. The cover is typically made from ionomer resins, balata, or urethane, among other materials. Ionomer covers, particularly harder ionomers, offer some protection against the penetration of water vapor. However, it is more difficult to impart spin to balls with hard covers. Conventional urethane covers, on the other hand, while providing better ball control, offer less resistance to water vapor than ionomer covers.
Several prior patents have addressed the water vapor absorption problem. U.S. Pat. No. 5,820,488 discloses a golf ball with a solid inner core, an outer core layer, and a water vapor barrier layer disposed therebetween. The water vapor barrier layer preferably has a water vapor transmission rate (“WVTR”) lower than that of the cover layer. The water vapor barrier layer can be a polyvinylidene chloride (“PVDC”) layer. It can also be formed by an in situ reaction between a barrier-forming material and the outer surface of the core. Alternatively, the water vapor barrier layer can be a vermiculite layer. U.S. Pat. Nos. 5,885,172 and 6,132,324 disclose, among other things, a golf ball with a polybutadiene or wound core with an ionomer resin inner cover and a relatively soft outer cover. The hard ionomer inner cover offers some resistance to water vapor penetration and the soft outer cover provides the desirable ball control.
There is still a need, however, for an efficient and effective composition that can replace the conventional ionomer-based composition for a golf ball layer. The present invention is direct to such a composition that can provide a non-ionomeric layer having improved flexural modulus, material hardness, and water vapor barrier property.